Method and apparatus for cleaning grinding work chuck using a scraper

ABSTRACT

A scraper assembly for removing debris deposited on the surface of a porous work chuck during a wafer grinding process.

RELATED APPLICATIONS

This Application is based on Provisional Application No. 61/632,262 filed on Jan. 23, 2012.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for cleaning the porous ceramic grind work chuck used in semiconductor wafer grinding machines.

2. Background of the Invention

U.S. Pat. No. 7,118,446, issued to Thomas A. Walsh and Salman Kassir and assigned to the assignee of the present invention exemplifies the status of prior art grinder apparatus technology. A chuck is provided in the apparatus to hold the work piece in place so that the work piece does not slip or otherwise move while being shaped by a grind wheel.

The chuck is porous i.e. holes are drilled therethrough it or otherwise comprises a porous material; a partial vacuum being provided below the chuck to hold the work piece in place. Coolant is pumped directly onto an area of contact between a grind wheel and the workpiece surface, providing cooling and cleaning of grind debris (swarf) from the surface of the workpiece.

During the grinding process, vacuum is applied through the porous portion of the work chuck to hold the wafer. If there is a particle (from the work chuck or from the incoming wafer) between the bottom of the wafer and the top of the work chuck, a crack in the wafer will be produced. This type of crack is called a “star crack” and propagating cracks originate at the particle.

Additionally, the wafers themselves may introduce particles onto the work chuck. The particles can lead to star cracks and/or non-uniformities in the grind.

What is thus desired is to provide a work chuck cleaning particle removal procedure wherein the cleaning can be done either automatically or manually.

SUMMARY OF THE INVENTION

The present invention provides method and apparatus for removing particles from the surface of a chuck used to hold a workpiece, such as a wafer, in position during grinding, the process being accomplished manually or automatically. In particular, a scraper assembly is positioned within a wafer grinder apparatus adjacent the edge of the work chuck. The assembly comprises a razor mechanism positioned on the face surface of a gimbal block, a plurality of brush members being positioned adjacent to the razor. The assembly further comprises a fluid source which, when activated, directs fluid to the chuck surface which in turn causes debris to be removed from work chuck surface. The razor mechanism is then moved from the center of the work chuck to the edge to remove any particles from the chuck surface. A source of sonic energy may be positioned on the assembly, or in the fluid path, the sonic energy loosening particles that may be tightly adhering to the chuck surface.

DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention as well as other objects and further features thereof, reference is made to the following description which is to be read in conjunction with the accompanying drawing therein:

FIGS. 1A and 1B are perspective and plan views, respectively, of a prior art grinder assembly modified to incorporate the scraper cleaning system of the present invention;

FIG. 2 is a perspective view illustrating the scraper assembly of the present invention positioned relative to the work chuck;

FIG. 3 is a partial perspective, sectional view illustrating the scraper assembly of the present invention;

FIG. 4 is similar to FIG. 3 showing the rotation of the scraper assembly about a gimbal point, the arrow showing the direction of motion of the work chuck;

FIG. 5 is a perspective view of the scraper assembly of FIGS. 2, 3 and 4 illustrating the face of the gimbal block with the razor and brushes shown;

FIG. 6 illustrates, in simplified form, how the present invention can be incorporated with the prior art grinding apparatus;

FIGS. 7( a)-7(c) illustrate various configurations for the scraper blade; and

FIG. 8 illustrates a preferred mounting assembly to hold the scrapper blade while cleaning the chuck surface.

DESCRIPTION OF THE INVENTION

In order to put the present invention in proper perspective, FIGS. 1A and 1B illustrate a prior art grinder assembly, such as that disclosed in the '446 patent, modified to incorporate the cleaner assembly of the present invention.

Referring to FIGS. 1A and 1B, shown are perspective and plan views respectively of the compact grinder assembly 100 disclosed in the '446 patent. Shown is a grind spindle 102, a spindle support column 104, a work spindle 106, a cabinet 108, a splash pan 110, a work chuck 112, a thickness probe 111, a ball screw assembly 114, a bed portion 118, rails 120 and a ball screw 122.

The grind spindle 102 is coupled with the spindle support column 104, and the spindle support column 104 is engaged with the rails 120 and the ball screw 122. The cabinet 108 supports the rails 120, balls screw 122, the work spindle 106 and the splash pan 110. The thickness probe 111 is coupled with the work spindle 106 and is shown positioned above the work chuck 112.

The grind spindle 102 is moved along a vertical axis by the ball screw assembly 114 and includes at least one grinding wheel (not shown) in order to shape a work piece, for example, semiconductor wafers.

The work chuck 112 holds the work piece in place so that the work piece does not slip while rotating and being shaped by a grinding wheel of the grind spindle 102. For example, the work chuck 112 is porous, e.g. it has holes drilled through it or otherwise comprises a porous material, and a partial vacuum is provided by a device (not shown) positioned below the work chuck 112 to hold the work piece in place.

The spindle support column 104, supports the grind spindle 102, and is moveably engaged with the rails 120, bed 118 and ball screw 122, to translate back and forth in a horizontal direction. Specifically, the spindle support column 104, and the grind spindle 102 move with respect to the cabinet 108, the work spindle 106, and thus a surface of a stationary work piece attached on the work chuck 112.

The ability to translate the grind spindle assembly 102 allows shaping of a work piece to be achieved on both a face and an edge of the work piece with a single machine. Specifically, a grinding wheel of the grind spindle 102 is first positioned over an edge of the work piece and then moved into contact with the edge of the work piece until the edge is shaped as desired. The grind spindle 102 is then raised vertically above the work piece, translated horizontally over a face of the work piece so the grinding wheel is positioned over the face of the work piece, and then the grinding wheel is then placed in contact with the face of the work piece by lowering the grind spindle 102 until the grinding wheel is in contact with a portion of the face of the work piece, typically contact with the center of the wafer mounted on work chuck.

Referring to FIG. 2, the work chuck scraper assembly 200 of the present invention is positioned above the top surface of work chuck 112. The backflush operation that is part of the process disclosed in the '446 patent cooperatively operates with assembly 200, the former forcing trapped particles from the bottom of the work chuck whereas assembly 200 removes trapped particles from the top surface of the work chuck 112. Particles may be trapped in pores anywhere on the work chuck surface. The scraper devices may be manipulated across the entire work chuck face as the work chuck rotates to clean the entire wafer surface.

FIG. 3 shows details of one embodiment of the structure of assembly 200 (work chuck 112 is supported on member 113). Specifically, a scraper mechanism 210, illustrated as a razor in the embodiment illustrated, is mounted within stationary (relative to gimbal block 206) housing 204 forming a spherical gimbaling surface. A port (not shown) may also be mounted within housing 204, water or other liquid being supplied to the port to aid in carrying debris off the top surface of the work chuck. Seal 212 is positioned around a portion of the circumference of housing 204 as illustrated and a gimbal block 206 with a matching spherical surface is cooperated with and is secured within housing 204. A set screw 208 functions to secure the scraper into the gimbal block. The angle of the scraper to the work chuck is defined by the angle machined into the gimbal block. The set screw can also be used to allow setting of the scraper depth. A plurality of brush bristles 214 project from the surface 220 of gimbal block 206. Although razor 210 is illustrated positioned at the perimeter of face portion 220, the razor may be positioned at the center surrounded by the brush bristles 214. As noted hereinabove, an alternate technique using liquid to cause assembly 200 to hover above the work chuck surface can be utilized, this technique being used in conjunction with the bristles 214 which provide stability and spacing. Although the preferred operating position of razor 210 is as shown in FIG. 2, the razor can be moved anywhere on the work chuck face as long s orientation of the blade to the rotation direction is maintained. Further, razor 210 is designed to operate on different materials that comprise the work chuck surface.

Referring to FIG. 4, as work chuck 112 rotates under assembly 200 as illustrated by motion arrow B, a side force, illustrated by arrow A, is induced on the assembly. In particular, the side force is generated by the relative motion of the chuck surface 202 under the assembly or by the movement of the indexing table (not shown) that supports the chuck spindle mechanism. In addition, the side force could also be caused by the scraping device itself. Since the projected gimbal point 215, or center of rotation, is below the top surface of work chuck 202, the leading edge of assembly 200 will not impact surface 201 due to the direction of the resulting moment. In particular, the projected gimbal mechanism moment prevents the leading edge of assembly 200 from digging into the top surface of work chuck 202. Since the projected gimbal point is below the surface of the work chuck, side force A (in essence, caused by friction between the moving parts) is exerted on assembly 200, the leading edge will rotate upward instead of downward into the surface of work chuck 202. A rotational driving mechanism 213 comprising slot and drive pin 217, ensures that the blade is pointed in the correct direction.

The operation of the assembly 200 is shown in more detail in FIG. 5. As noted above, in addition to brushes (bristles) 214, fluid flow may be emitted through openings 232 and impinge on the surface of work chuck 112 causing assembly 200 to hover above the surface. The work chuck back flush could also be used to hover assembly 200 above the surface of the work chuck.

Work chuck 112 then is then rotated and the tip of the razor 210 (adjusted so that the tip engages its surface) causing the projecting debris particles to be removed.

Assembly 200 may be activated manually for most applications. However, if cleaning is required for every work piece, a control signal can be provided from the system control software to actuate the scraper assembly 200 before grinding each wafer (or every Nth wafer).

The operative cycle of assembly 200 is as follows:

After the wafer is removed from the top surface of work chuck 202, the work chuck blow-off (air) and back flush fluid, such as distilled water is turned on to purge the majority of the particulates that were sucked into the porous work chuck material during the grinding cycle. During this process, the work chuck is spinned causing the particles to be removed from its edge. After the majority of particulates now have been removed, scraper assembly 200 is then actuated and placed on the work chuck. Most of the remaining particulates will be trapped where the perimeter of the wafer made contact with the porous section of work chuck 202. Scraper assembly 200 typically starts in the center of the work chuck 202 and moves radially outward until it reaches the location where the most of the particulates are trapped. The scraper assembly 200 stays in this position as work chuck 202 slowly rotates. After the user defined scraper time has been reached, the scraper assembly will lift and rotate back to the center home position or away from the work chuck. Note that assembly 200 never (other than the tip of razor 210 touches the surface of the work chuck because of brushes 214, and/or if required, a layer of water. Note that the scraper device itself may also be rotated although this is not the preferred technique.

FIG. 6 is a simplified diagram illustrating how the scraper assembly 200 of the present invention is typically coupled to the grinder apparatus shown in FIGS. 1A and 1B. In particular, housing 400 is secured to arm 402, of the grinder tool via mounting screws 404 and 406. Within housing 400 is a spring loaded actuator 408 coupled to blade 410. Work chuck spindle 412 rotates the work chuck in a conventional manner. A bearing or bushing (not shown) is coupled between actuator 408 and special blade 410 to resist lateral motion but allow up/down movement. Alternately, a motor could be used to drive blade 410.

FIG. 7( a) illustrates two possible alternate shapes for the blade 410, a flat blade 416 and a cone shaped blade 418. FIG. 7( b) shows flat blade 416 with a brush support 420 and FIG. 7( c) illustrates a curved blade 422.

FIG. 8 illustrates an alternative device 500 to mount scraper blade 502. Spring 504 provides the force to hold blade 502 against the surface of the work chuck as it rotates. The blade 502 is designed to cover the center to edge of the entire work chuck.

While the invention has been described with reference to its preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its essential teachings. 

What is claimed is:
 1. A method for cleaning particles from the surface of a circular cylinder shaped and rotatable work chuck used in a grind apparatus comprising the steps of: providing a work chuck having first and second surfaces, said work chuck being operable in conjunction with said grind apparatus; positioning a scraper device adjacent said first surface of said work chuck; and activating said scraper device whereby said particles are substantially removed from the first surface of said work chuck.
 2. The method of claim 1 wherein said work chuck has an edge portion along its perimeter.
 3. The method of claim 2 wherein said scraper device is positioned above said edge portion of said work chuck.
 4. A grind apparatus for grinding a surface of a workpiece comprising: a grind wheel; a porous work chuck having top and bottom surfaces; means for rotating said work chuck and said grind wheel; a scraper device positioned adjacent to said top surface of said work chuck; means for moving said scraper device across the top surface of said work chuck; and means for energizing said scraper device whereby particles on the top surface of said work chuck remaining after grinding of said workpiece are substantially removed. 